As the semiconductor devices keeps scaling down in size, three-dimensional multi-gate structures, such as the fin-type field effect transistors (FinFETs), have been developed to replace planar Complementary Metal Oxide Semiconductor (CMOS) devices. A structural feature of the FinFET is the silicon-based fin that extends upright from the surface of the substrate, and the gate wrapping around the conducting channel that is formed by the fin further provides a better electrical control over the channel.
Currently, FinFETs have applied to various applications. In some high power applications, the currently fabricated FinFETs do not meet the high power requirements. Accordingly, how to increase saturation current and current density of FinFETs is important to those skilled in the art.